#include<bits/stdc++.h>
#define XH(i,a,b) for(int i=a;i<b;++i)
#define XXH(i,a,b) for(int i=a-1;i>=b;--i)
#define LL long long
using namespace std;
int tmpINT; string tmpSTRING; char tmpCHAR; double tmpDOUBLE; LL tmpLONGLONG;

double X,Y,R;

int main(){
	cin>>X>>Y>>R;
	int left = (ceil)(X-R);
	int right = (floor)(X+R);
	int low,high;

	LL ans = 0;
	for (double i = left ; i <= right ; ++i){
		tmpDOUBLE = sqrt(R*R - (X - i)*(X - i));
		// cout<<"tmpDOUBLE="<<tmpDOUBLE<<endl;
		high = (floor)(tmpDOUBLE + Y);
		low = (ceil)(Y - tmpDOUBLE);
		// printf("high = %I64d, low = %I64d\n",high,low );
		ans += high - low + 1;	
	}
		
	printf("%I64d\n", ans);
	
	return 0;
}
